The overall aim of this research project is to define the maternal contribution to early mammalian development. We aim to characterize the RNA and protein components of the mouse egg, to examine their accumulation during oocyte growth, and to elucidate their role during embryogenesis. In the next year, electron microscopic analysis will be used to complement our biochemical evidence for storage of mouse egg ribosomes in unusual lattice structures seen in the electron microscope. We will attempt to characterize the buoyant density of mouse egg messenger ribonucleoprotein particles, and to follow the flow of maternal messenger RNP and ribosomes into polysomes during early embryogenesis. The retained maternal RNA will be localised in the embryo by autoradiography with special focus on whether maternal RNA enters the nucleus and whether the retention of maternal RNA is similar in the inner cell mass and trophoblast. Finally, the accumulation of ribosomal RNA during oocyte growth will be measured by analysing the ribosomal RNA content of growing oocytes of different sizes using a labeled cDNA complementary to ribosomal RNA.